Phase shift keying communication system



Aug. 9, 1966 M. D. M FARLANE ETAL 3,265,813

PHASE SHIFT KEYING COMMUNICATION SYSTEM Original Flled April 28, 1958 4SheetsSheet 1 FIG. I 12 L9 /8 20 I 1 CARR|ER TRANSMITTER OS-GIILLATORMODULATOR OUTPUT STAGE STAGE v STAGE MODULATOR KEYING STAGE RECEIVERPHASE INPUT DETECTOR STAGE STAGE 46 V I) 44 FULL WAVE gg i FREQUENCYRECTIFIER CIRCU'T DIVIDER M48 F/Go 3 MODULATOR KEY l N G d/ [5 STAGE MA74 11 a v 0. m Mun/v5 INVENTORS C ECl L A.CRQFTS BY MLQ Z Q Aug. 9, 1966M. D.MFARLANE ETAL.

PHASE SHIFT KEYING COMMUNICATION SYSTEM Original iled April 28, 1958 4Sheets-Sheet 2 -FIG. 4

FIG. 5B

FI6.5C

- FIG. 5a

OPEN

CLOSED l I f l l l l l l v INVENTORJ may/VAL] 7 rflcF/ZKL/M/E CEc/LACILAFTS 9. 1966 M. D. MCFARLANE ETAL 3,265,313

PHASE SHIFT KEYING COMMUNICATION SYSTEM Original med April 1958 4Sheets-Sheet s FIG. 6

2 I02 CARRIER THREE PHASE TRANSMITTER 94 ,OSClLLATOR r MODULATOR OUTPUTSTAGE STAGE GE MODULATOR KEYING STAGE 4 MODULATOR KEYING 98 STAGERECEIVER FIG 8 PHASE .NPUT DETECTOR STAGE STAGE x I I A NG DIFFERNTIATINPARALLEL FREQ- PH ASE RESONANTLF SHIF'HNG CIRC I CIRCUIT cmcurr DIVIDERSTAGE FIG. 9A

FIG. 9B

1 ,42 FIG'QC V U INVENTORS' m c gziz fiazza FIG. 90 BY Aug. 9, 1966 M.D. M FARLANE ETAL PHASE SHIFT KEYING COMMUNICATION SYSTEM Original FiledApril 28, 1958 4 She'ets-Sheet 4 I46 FIG. /0 /5 LOCAL J MODULATOR I94OSCILLATOR KEYING 1 STAGE RECEIVER INPUT A [65 STAGE, SAT/E I84 RECEIVERgvgl xgrg ADDITION INPUT 7 smee STAGE CIRCUIT L K AUXILIARY PHASEDETECTOR Q PARALLE T I82 SQUARING DIFFERENTIATING FREQ PHASE CIRCUIT]CIRCUIT, cmcugr SMFTING STAGE 172 174 ms I78 30 PHASE A" FIG i l 2 I86/l\ i PHASE 8' i I I88 /T\ I 1 PHASE "0 I l l i I I NVENTORJ' CELILA.C!ZAFT$ United States Patent 3,265,813 PHASE SHIFT KEYINGCOMMUNICATION SYSTEM Maynard D. McFarlane, Corona Del Mar, and Cecil A.

Crafts, Santa Ana, Calif., assignors to Rohertshaw Controls Company,Richmond, Va., a corporation of Delaware Original application Apr. 28,1958, Ser. No. 731,334, now Patent No. 3,112,448, dated Nov. 26, 1963..Divided and this application May 4, 1962, Ser. No. 192,568

11 Claims. (Cl. 178-88) This invention relates to communication systems,and more particularly to a system and method employing phase shiftkeying for modulating a carrier wave. It is a division of patentapplication Serial No. 731,334, filed April 28, '1958, now Patent No.3,112,448, by Maynard D. McFarlane and Cecil A. Crafts.

In many modern day phase shift communication systems, it is necessary topropagate a separate reference signal which is employed in the receiverfor retrieving the information implicit in the modulated signal. In suchsystems,the atmospheric attenuations and diminutions in the signalstrength of the reference signal present a large possibility for error.

The present invention contemplates method and apparatus for use in keyedtype communication systems such as teletype and binary data transmissionsystem. In one aspect of the invention, the information which it isdesired to transmit is impressed upon a carrier wave by periodicallyeffecting a phase shift of 180 in the wave. The reference signal isderived from the modulated carrier wave at the receiver, and therequirement for a separate reference signal is entirely eliminated.

By employing this method of operation most of the technical deficiencesof prior art phase shift systems are avoided. For instance, a verysubstantial reduction in band width is achieved, as compared toconventional systems which modulate either the frequency or amplitude ofa carrier signal. This is because the only side bands generated in thepropagation of the signal are those produced by the keying frequency.

The accomplishment of such information transfer by means of a singlefrequency eliminates the disadvantages which invariably attend the useof a pilot carrier in prior art systems. In addition, the derivation ofthe reference signal directly from the modulated signal detected at thereceiver eliminates the lack of stability which often characterized theuse of artificial reference signals in many known communication systems.

According to another aspect of the invention, the information in whichit is desired to transmit is impressed upon a carrier wave byperiodically providing phase displacements of 0", 120, and 240 in thecarrier wave. By practicing still another aspect of the presentinvention, the information to be propagated is impressed upon a carrierwave by selectively effecting phase displacements of 0, 90, 180, and270. Moreover, in addition to providing method and apparatus forretrieving information from a carrier by distinguishing between therespective phases thereof, the present invention provides method andapparatus for distinguishing between the various phase signals on a timebasis.

Accordingly, therefore, a primary object of this invention is to employa phase modulated carrier wave in a system which has the capacity forderiving a phase reference signal therefrom.

Another object of this invention is to transmit information in acommunication system by means of successive phase reversals in a carrierWave.

A further object of this invention is to convey data by means ofpolarity permutations in a keyed carrier wave.

,8 13' Patented August 9, 1 966 "ice A still further object of thisinvention is to convey information over a distance by means of a keyedcarrier wave without the necessity for simultaneously propagating aseparate reference signal therewith.

These and other objects and advantages of the present invention willbecome apparent by referring to the following detailed description anddrawings in which:

'FIG. 1 is a block diagram of the transmitter provided by the presentinvention;

FIG. 2 is a block diagram of the receiver circuity of the presentinvention;

FIG. 3 is a wiring diagram of the circuitry and components of themodulator stage which is used in practicing the invention;

FIG. 4 is a wiring diagram of the circuitry and interconnectionsprovided within the receiver circuit;

FIG. 5A illustrates the form of the modulated carrier Wave;

FIG. 5B shows the time relationship between open and closed switchingpositions within the modulator stage and the carrier wave immediatelythereabove;

FIG. 5C illustrates the form of the modulated carrier wave after fullwave rectification within the receiver;

FIG. 5D illustrates the appearance of the double frequency signal whichis produced within the receiver by passing the rectified signal shown inFIG. 5C through a resonant circuit;

FIG. 6 is a block diagram of the transmitter utilized for propagating acarrier wave characterized bythree input conditions or phase positions;

FIG. 7 is a wiring diagram of the circuitry and components of the threephase modulator stage employed in FIG. 6;

FIG. 8 is a block diagram of the receiver circuitry employed inabstracting information from a three phase modluated carrier 'Wave;

FIG. 9A through FIG. 9D indicate the successive changes experienced bythe carrier wave form in traversing portions of the receiver circuitryshown in FIG. 8;

FIG. 10 is a wiring diagram of the circuitry and interconnectionsprovided by the invention for selectively effecting four successivephase displacements in a carrier wave;

FIG. 11 is a block diagram of the receiver circuitry which is utilizedin retrieving a message from a four phase modulated carrier wave;

FIG. 12 shows diagrammatically the interrelationships between severalwave forms in a three phase modulated system, and is used to explain theseparation of signals in the received carrier on a time base; and

FIG. 13 is a block diagram of the apparatus employed in accomplishingelectronic commutation of the incoming signals.

Referring more particularly to the drawings, in FIG. 1 the numeral 10indicates generally the components of the transmitter used in thepresent invention. The transmitter 10 will be seen to include a carrieroscillator stage 12. The oscillator stage 12 is characterized by theability to produce an alternating current signal of predeterminedfrequency. The oscillatory signal produced by the stage 12 is applied asan input signal to modulator stage 14.

The modulator stage 14 includes circuitry and components for rapidlyreversing the phase of the carrier signal by Although the circuitry foraccomplishing this phase reversal forms an integral part of the presentinvention, it should be appreciated that the reception of signals from aconventional type of phase shift keying transmitter is possible byemploying the receiver system according to the present invention.

The periodic reversal of the carrier signal by the modulator stage iseffected in response to signals provided by a modulator keying stage 16.The modulator keying stage 16 may include suitable electromechanicalmeans for rapidly shunting one or more of the impedance elements withinthe modulator stage. It will be appreciated that space dischargedevices, gas tubes, transistors or the like would be equally feasiblefor this purpose.

The stage 14, shown in detail in FIG. 3, includes a switch 36 in orderto accomplish the phase reversals in the carrier. The term switch asused in this connection may comprehend the several common types ofelectrical closures. One terminal of the switch 36 is connected to thegrounded junction between resistors 26 and 30. The opposite terminal ofthe switch 36 is connected between the resistors 28 and 30. When theswitch 36 is in the open position, the output of stage 14 takes the formof a positive electrical Wave; conversely, when the switch 36 .isclosed, the output of the stage is reversed by 180 that takes the formof a negative electrical wave. The modu lated carrier wave thus producedappears between the junction point of resistors 32 and 34 and ground.

The switch 36 which shunts resistor 30 in FIG. 3 is periodically openedand closed by means of the modulator keying stage 16 shown in FIG. 1.Although the switch 36 has been referred to in terms most apt for thedescription of a mechanical device, it should be understood that theswitching function which periodically shunts the resistor 30 may beaccomplished by space discharge devices, gaseous conduction devices, orthe like. For instance, the

. use of a pulsed thyratron tube, or the like to shunt the resistor 30would be included.

Turning to FIG. 2, the receiver circuitry includes a receiver antenna 38which samples the incoming modulated carrier wave. The receiver inputstage may receive ,energy directly from the transmitter via aconventional coaxial cable or the like. The signal received by theantenna 38 is applied to a receiver input stage 40. The

stage 40 may include suitable stages of amplification for compensatingfor any reductions in signal strength which have occurred during thepropagation of the carrier wave.

Moreover, stage 40 may include suitable impedance matching circuitry andthe like for insuring optimum energy transfer from the antenna, orcable, as the case may i. be.

The modulated signal which occurs at the output of l the stage 40 isapplied directly to a phase detector stage I 42. In order to retrievethe information implicit in the 1 modulated carrier, means are providedwithin the receiver circuit for developing a reference signal having awave form identical with that of the carrier wave before it has beenkeyed, or modulated.

In order to develop such a reference signal, the modulated signal fromthe receiver input stage 40 is applied to a full wave rectifier 44. Thesuccession of positive voltage -impulses produced by the full waverectifier 44 is then used to excite a parallel resonant circuit 46. Theresonant circuit 46 is tuned to the second harmonic of the frequencyproduced by the transmitter.

The parallel resonant circuit 46 is characterized by a high Q. This highQ resonant circuit carries on the action of deriving a reference signalduring momentary interruptions which occur in the reception of carrieras a result of keying transients or atmospheric fading. This, of course,is because of the cyclic interchange of energy which occurs between theinductance and capacitance elements in such a resonant circuit.

After the modulated carrier has been acted upon by l the full waverectifier 44 and the high Q parallel reso- 4 characterizes prior artphase shift systems of the type which employ a separate referencesignal.

The frequency reduction which is applied to the output of the resonantcircuit is accomplished by means of a frequency divider 48. The divider48 may comprise a conventional circuit such as a bistable multivibrator,or the like which derives an output signal in the form of a sub-multipleof the input frequency.

The output potential of the divider 48 comprises an oscillatory signalhaving the same frequency as the carrier wave and constant phase. Thissignal is used as a reference signal within the phase detector stage 42.The stage 42 compares the phase of the incoming modulated signal withthat of the constant phase reference signal provided by the frequencydivider 48, and develops an output potential related to the differencestherebetween.

The circuitry and interconnections for accomplishing the functions setforth immediately above are illustrated in FIG. 4, including a couplingtransformer 50 in the lefthand portion thereof. The primary winding ofthe transformer 50 may receive an input signal from the receiver inputstage 40. The transformer 50 is provided with a pair of secondarywindings 52 and 54. One end of the secondary winding 52 isinterconnected to the opposite end by means of a pair of seriesconnected capacitors 56 and 58. The capacitor 56 is shunted by aresistor 60, and the capacitor 58 is shunted by a resistor 62. Thewinding 52 is provided with a tap terminal 64 for purposes to beexplained more fully below. This secondary winding taken in conjunctionwith the component capacitors and resistors comprises a phase detectorwhich is able to compare the phase of the reference signal with that ofthe modulated signal.

The secondary winding 54 is closed upon itself through a pair of seriesconnected oppositely-poled diode elements 66 and 68. The commonconnection between the diode elements 66 and 68 is grounded through aresistor 70. The potential developed across resistor 70 is coupled to aparallel resonant circuit 46 through resistor 72. The resonant circuit46 includes a conventional inductance 74 and capacitance 76. Onejunction between the inductance and capacitance is grounded, and theopposite junction is connected to excite a conventional multivibrator 78comprised of a pair of space discharge devices V1 and V2 with associatedimpedance elements.

The resonant circuit 46 is connected to the control grid of the spacedischarge device V1. The anode of V1 is interconnected to the controlgrid electrode of the space discharge device V2 via a couplingcapacitor. The cathode elements of the respective discharge devices arecon- .nected in common and coupled to ground through a resistor 80. Thecontrol grid of the device V2 is connected to the commonly connectedcathodes via resistor 82. Operating potential is supplied to thedischarge devices V1 and V2 through plate load resistors 84 and 86,respectively. The output wave form developed by the multivibrator 78 iscapacitor coupled to the primary of an output transformer 88. It will beappreciated that the function of the multivibrator 78 is to reduce by afactor of 2 the frequency of the oscillatory signal developed by theresonant circuit 46.

It will now be evident that the diodes 66 and 68 acting in conjunctionwith the resonant circuit 46 and the multivibrator 78 act to provide areference signal which has a wave form substantially identical with thatproduced by the oscillator stage 12 within the transmitter. Thisunmodulated wave form is inductively coupled back to the phase detectingstage 42 by means of transformer 88 for comparison with the modulatedcarrier wave therein. Thus, one terminal of the secondary winding oftransformer 88 is connected to the tap terminal 64 provided on winding52. The opposite end of the secondary winding of transformer 88 isconnected to the junction point between capacitors 56 and 5 8. Theoutput signal developed by the phase detector 42 is made available onthe conductor 90, shown in the uppermost portion of the drawing.

The inter-relationships between the various wave forms whichcharacterize the invention are illustrated in FIGS. 5A, 5B, 5C and 5D.Thus, in FIG. 5A, successive positive cycles of the carrier frequencyare seen to occur while the switch '36 occupies an open position. Whenthe switch 36 is closed, as evidenced by the negative rectangle in FIG.5B, the phase of the carrier shifts by 180 and becomes negative.

In FIG. 5C, the successive nodes or voltage loops provided by therectifier 4-4 are illustrated. Directly beneath -FIG. 5C, the doublefrequency sinusoidal signal produced by the resonant circuit 46 isshown. It will be recalled from the earlier portions of the detaileddescription that the double frequency wave form shown in FIG. 5Dexhibits no modulation, and forms 2. reference signal after frequencyreduction within the multivibrator stage 78. As earlier explained, thereference signal thus developed is free of the atmospheric distortionand attenuation which accompanies the propagation of -a separatereference signal in prior art systems.

As shown in FIG. 6, the numeral 92 has been used to indicate generallyan embodiment of the invention suitable for use in transmittingintelligence with three different input conditions or phase positions ina carrier wave. The three input conditions or phase positions which areprovided by the circuitry shown in FIG. 6 take the form of sinusoidalcarrier wave signals having phase displacements of 0, 120, and 240 withreference to zero time.

The system for producing these phase displaced signals will be seen toinclude a carrier oscillator stage 94. The oscillator stage 94 ischaracterized by the ability to produce an alternating current outputsignal of predetermined amplitude and frequency. The output signal thusprovided is applied to a three-phase modulator stage 96 which includescircuitry and components for rapidly shifting the phase of the carriersignal between the respective 0, 120, and 240 phase positions. It

should be appreciated that the circuitry and components located withinstage 96 for the purpose of accomplishing these rapid variations in thephase of the carrier form an integral part of the present invention andwill be described in detail hereinafter.

The modulator stage 96 accomplishes the selective variation in the phasecarrier signal in accordance with the operation of a modulator keyingstage 98. The modulator keying stage 98 may include suitable electronicor electro-mechanical means for rapidly connecting and disconnecting therequisite values of impedance within the modulator stage in order toselectively provide the phase displaced sine wave signals necessary tothe transmission of intelligence contemplated by the invention.

The phase modulated carrier wave produced at the output terminals of thestage 96 is applied to a transmitter output stage 100. The stage 100 mayinclude conventional circuitry and components for amplifying orotherwise appropriately modifying the modulated carrier. Where it isintended to propagate the modulated signal through space as anelectromagnetic wave, the

output signal from stage 100 is coupled to an antenna 102. If desired,the output signals from stage .100 may be applied through a suitablecoaxial cable or the like to the intended reception site, rather than bymeans of space propagation from an antenna. The stage 100 will beunderstood in this connection to include suitable equipment forproviding optimum energy transfer to the antenna or cable, as the casemay be, and such equipment may comprise one or more stages ofconventional impedance matching circuitry.

One form. of the apparatus for selectively varying the phase of thecarrier wave is schematically illustrated in FIG. 7 and includes acoupling transformer .10 4. The primary winding of this transformer isconnected to receive the alternating carrier signal developed by theoscillator stage 94.

One end of the secondary winding of coupling transformer 104 iselectrically connected through a resistor 106 to the movable arm of athree position switch 108. The switch .108 may include a conventionalpivotally mounted electromechanical switch provided with a movablemember which is capable of successively engaging any one of the threeterminals. The opposite end of the secondary winding of transformer 104is connected through a capacitor 110 to terminal 112 of the threeposition switch. This end of the secondary winding is also connected toone end of an inductor 114 which terminates at terminal 116 of the sameswitch. It will be observed that the movable arm of the switch maycontact an intermediate terminal 118 located between the terminals 116and 112. The signal from trans-former 104 which is sampled by themovable element of the switch 108 is coupled to the subsequent stages ofcircuitry via an output conduct-or 120.

In order to provide a pair of sinusoidal wave forms which differ by 120and 240 from the initial zero phase position of the carrier, it isnecessary to provide definite values of impedance for the capacitor 110and the inductor 1 14. The initial zero phase position is, of course,generated when the movable element of switch 108 engages theintermediate terminal 118. The value of the reactance for the inductor114 must be such that, taken in conjunction with the other parameters inthe circuit, a wave form displaced by 120 from the zero phase positionis provided whenever the movable arm of the three position switchengages contact 116.

The capacitive reactance of the condenser 110 is proportioned to equalthe inductive reactance of the inductor i114. When the movable arm ofthe three position switch 108 receives potential from terminal 112, the120 phase shift thus will be effected in a direction opposite to thatprovided by the inductor 114. For open circuit conditions when themovable arm of the three position switch engages contact 118, the zerophase shift carrier wave is inductively transferred directly fromtransformer 104 to the output conduct-or 120 without the use of anyphase shifting impedance elements.

In FIG. 8, the receiver circuitry which is utilized in retrievingintelligence from the three phase modulated carrier is shown. Thiscircuitry includes a receiver antenna 122 which samples the incomingmodulated carrier wave and applies it to a receiver input stage 124. Thestage 124 may also receive energy directly from the transmitter via aconventional coaxial cable or the like. The stage 124 may includesuitable amplification circuitry which compensates for any reductions insignal strength occurring during the propagation of the carrier wave.Appropriate impedance matching circuitry and the like for insuringoptimum energy transfer from the antenna, or cable, may also be providedwithin the stage 124.

The modulated signal which appears at the output of stage 124 is applieddirectly to a phase detector stage 126. In order to develop the messageimplicit in the phase modulated carrier, means are provided within thereceiver circuit for developing a reference signal which duplicates thewave form of the carrier wave as it appeared prior to being modulated.

In order to develop a reference signal, the modulated signal from thereceiver input stage 124 is applied to a squaring circuit 128. Theoutput square wave derived by circuit 128 is applied to adifferentiating circuit 130. The circuit 130 develops a time-spacedseries of voltage spikes which occur simultaneously with the changes insign in the output square wave developed by the circuit 128. Thesevoltage spikes are coupled to a parallel resonant circuit 132 which istuned to the third harmonic of the carrier wave frequency. From theresonant circuit 132, the triple frequency output sine wave is appliedto a frequency divider 134.. The divider 134 may comprise phase detector126 will be zero.

a conventional count-down circuit which has the capacity to produce anoutput signal at a frequency which is a submultiple of the inputfrequency.

The output potential of the frequency divider 134 comprises anoscillatory signal having the same frequency as the carrier wave andconstant phase. This signal is utilized as a reference signal within thereceiver after passage through a phase shifting stage 136. The phaseshifting stage 136 includes circuitry and components for shifting thephase of the oscillatory input signal by 30. By this means the output ofthe divider is displaced 90 out of phase with the input signal, at oneof the input phase conditions. Comparison of the phase shifted referencesignal produced by stage 136 with the three phase modulated carrier isaccomplished within the phase detector stage 126.

For the input phase with which the reference signal now exhibits a 90phase displacement, the output of the On the other hand, the other twophase modulated positions of the carrier Wave will result in positivelyand negatively polarized output potentials respectively. By this means,the inventive feature of-transferring information with the three inputconditions or phase positions is provided.

By referring to the wave forms shown in FIG. 9A through FIG. 9D, thesuccessive changes in the signal accomplished by the system shown inFIG. 8 in order to develop a reference signal from the modulated carrierwill be more readily appreciated. In FIG. 9A, the sinus- .oidal signalappearing at the output of the receiver input stage 124 has beendesignated by the reference numeral 138. Directly beneath FIG. 9A, theappearance of the wave form produced by the squaring circuit 128 hasbeen identified in FIG. 9B by the reference numeral 140.

In FIG. 9C, the wave form of a third harmonic sine wave produced by theparallel resonant circuit 132 has been identified by the referencenumeral 142. Below this triple frequency sine wave, a group ofoutputvoltage spikes 144 developed by the differentiating circuit 130have been illustrated in FIG. 9D. It will be appreciated in thisconnection that the differentiation which produces the spikes 144 inFIG. 9D occurs prior to the production of the waveform 142 within theresonant circuit.

The correspondence between the zero axis crossings of the third harmonicsine Wave in FIG. 9C and the voltage spikes in FIG. 9D is exploited inthe redevelopment of the reference signal. Thus, reference to FIGS. 9Dand 90 will show that regardless of whether the input phase displacementis 120, or 240 the voltage spikes 144 occur at the same relative timewith respect to the third harmonic wave form shown in FIG. 9C. Thismeans that the energizing pulses which are supplied to the parallelresonant circuit 132 are characterized by a constant time spacing whichis not disturbed by the keying or modulating intervals.

Continuing with the description of the invention, and more particularlywith the technique for employing four input conditions or phasepositions, reference will now be made to FIG. 10 wherein the referencenumeral 146 indicates generally a four phase modulator stage. Thecircuitry of FIG. 10 is employed in a transmitter stage capable ofselectively altering the phase of a reference carrier wave by 90increments. Because of the basic similarity between the three phasetransmitter shown diagrammatically in FIG. 6 and the four phasetransmitter which utilizes the circuitry shown in FIG. 10, a separateblock diagram of the complete four phase transmitter has not beenillustrated. It is sufficient for purposes of the detailed descriptionto indicate that the block diagram of the complete four phasetransmitter is similar to that shown in FIG. 6 except for thesubstitution of a four phase modulator phase between the carrieroscillator stage and the transmitter output stage.

Referring again to FIG. 10, the four phase modulator stage shownincludes a coupling transformer 148. The

secondary of this transformer 148 is closed upon itself by means of aresistor 150 and capacitor 152 connected in series. It will be notedthat the secondary winding of transformer 148 is provided with agrounded center tap.

The common junction between resistor 150 and capacitor 152 isconductively connected to the pivot point of a two-pole switch 154. Thepivot point of switch 154 is connected to the control grid of a vacuumtube V1. The switch 154 is provided on the lefthand side with a terminal156. On the righthand side, a terminal 158 is similarly provided. Theterminals 156 and 158 are connected to the upper and lower ends of thesecondary winding of the transformer 148 respectively. The closure ofthe lefthand pole of the switch 154 results in shunting the resistor150. In like manner, the closure of the righthand pole of switch 154results in shunting the capacitor 152.

The energizing potentials present at the control grid of the tube V1produce a sinusoidal plate current in the primary winding of thetransformer 160. The secondary winding of transformer 160 is closed uponitself by means of a tapped resistor 161 and is provided with a groundedcenter tap. The resistor 161 is provided with the tap junction toexpedite grounding any selected portion of the resistor. The tapjunction on resistor 161 is connected to the movable pole of a switch162 shown immediately to the left. The switch 162 is provided with acontact 163 conductively connected to the juncture between the upperends of resistor 161 and the secondary winding of trans former 160.

In operation, the shunting of capacitor 152 by means of the righthandpole of switch 154 provides a 0 phase shift on the output conductor 164.It will be observed that the conductor 164 is connected to the juncturepoint between a pair of resistors 167 and 169. The opposite ends ofthese resistors are connected to the contact 163 and the lower end ofthe resistor 161, respectively. In the rest condition, with the poles ofswitches 154 and 162 in the open position, the sine wave produced onconductor 164 is characterized by a 90 phase shift. When resistor 150 isshunted by the engagement of the lefthand pole of switch 154 withcontact 156, the output signal thus provided differs from the referencephase by Finally, movement of switch 162 into engagement with'contact163 gives rise to an output sine wave displaced by 270 from thereference phase.

It will be observed that the selective closure of the movable poles ofswitches 154 and 162 is accomplished by means of a modulator keyingstage indicated diagrammatically in FIG. 10 by the reference numeral165. It should be understood that the invention is not limited tomechanical switching means for shunting the resistor 150, capacitor 152or the upper portion of tapped resistor 161. For instance, the use of apulsed thyratron or the like to provide a zero resistance path aroundany of these elements would be deemed to fall squarely within thepurview of the appended claims.

The circuitry and components for retrieving the message from the fourphase modulated carriers is indicated diagrammatically in FIG. 11. Asshown, the modulated signal sensed by antenna 166 is supplied to areceiver input stage 168. After suitable amplification and modificationin stage 168, the modulated signal is supplied to a phase detector stage170. The modulated signal is also applied to a squaring circuit 172illustrated directly beneath the input stage 168. The squared wave formthus produced is fed to a differentiating circuit 174 which produces aseries of time spaced voltage spikes. These voltage spikes from circuit174 are applied to a parallel resonant circuit 176, which is tuned tothe fourth harmonic of the carrier frequency. The output of the resonantcircuit 176 is applied to a frequency divider 178 comprised of circuitryfor developing an output frequency one fourth of the frequency of theinput signal applied thereto.

A portion of the reduced frequency potential from the frequency divider178 is applied directly to a phase shift- 9 ing stage 180. This outputpotential is also directly connected to the phase detector stage 170.The phase shifting stage 180 is employed for the purpose of effecting a90 shift in the phase of the reference voltage supplied thereto. Thephase shifted reference voltage thus derived is applied to an auxiliaryphase detecting stage 182.

One third of the output voltage from the auxiliary phase detector stageis algebraically added to the total output potential from the phasedetector stage 170 within an addition circuit 184. The circuit 184 mayemploy a conventional component characterized by the ability to producean output voltage representative of the sum of the input potentials.

Because of the use of the phase shifting stage 180 with the auxiliaryphase detector and addition circuit 184, the and 180 phase displacementsin the carrier will yield output potentials of positive and negativesign respectively. The 90 and 270 phase displacements will yield outputpotentials of positive and negative sign, but of one-third the magnitudeof the signal produced by the 0 and 180 phase displacements. By thismeans, four distance and nonambiguous values of receiver output voltageare produced to correspond with the four input phase shift values.

In FIG. 12, there is pictorially illustrated the wave forms of a threephase system. Phase A is represented as a sine wave 186 having zerophase shift. Phase B takes the form of a sine wave 188 having a 120phase shift and Phase C takes the form of a sine wave 190 having a 240phase shift. Although all of the phases are not transmittedsimultaneously, they have been depicted in FIG. 12 in this fashion inorder to clarify this aspect of the invention.

Below the respective sine waves 186, 188 and 190, -a

triple frequency sine wave 192 is shown. It will be ob- 188. In likemanner, the peaks 3, 6, and 9 of the triple frequency wave correspond.to definite peaks in the phase C sine wave 190. g a

It will now be appreciated that for the occurrence of each positive peakof the triple frequency wave, there will be positive peak in one of thecarrier waves, while the other carrier waves are characteriezd by eitherzero or negative amplitudes. This correlation between-positive peaks isexploited as a means of self-synchronism. Since the correspondingfundamental wave such as a phase A, phase B, or phase C can beidentified by ascertaining whether coincidence is established betweenthe peak of the fundamental wave and the first, second, or third peak ofthe triple frequency wave 192, it is possible to establish the relativephase which has been transmitted by identifying the particular group oftriple frequency waves which correspond to the received fundamental.

If the wave 186 in FIG. 12 be regarded as -a 1000 cycle per secondcarrier which may be periodically shifted by 120 and 240, the positivepeak of each of the received signals must invariably occur at timespacings of .001 second. Because of the 120 and 240 phase displacements,however, such positive peaks may be displaced at :0003 second by thephase shifting technique. Thus, the 0 phase shift wave 186 may be takenas providing positive peaks which occur at .001, .002 and .003 second,and so on. On the other hand, the 120 phase shifted wave 188 haspositive peaks which occur at .00033; .00133; .0023 3, etc. In likemanner, the 240 phase shifted wave 190 is characterized by positivepeaks which occur at .00066; .00166; .00266 second. By means of theelectronic commutator shown in FIG. 13, these timeincrements areexploited to separate the phase signals on a time basis.

In FIG. 13, the incoming energy is sampled by an antenna 194 and appliedto a receiver input stage 196. From the input stage 196, the phasemodulated wave-s are applied to a local oscillator 198. The oscillator198 serves to provide a frequency value three times that of the incomingfrequency, and is locked in with the transmitting frequency regardlessof the relative phase in which this frequency occurs. Moreover, theoscillator 198 provides a gating frequency by means of which the tubesin the ring gate 200 are energized. As a result of this gating, theincoming received signal energizes an appropriate local circuit whichcorresponds to a particular phase function.

The gate 200 may comprise a conventional counter which employs threenormally blocked counting units operated as gates. The triple frequencysignal from the oscillator 188 is applied to the counter circuitry sothat the positive or negative peaks cause the signal to advance one unitin the counting direction. Each individual tube of the ring gate whenthus energized will become conductive and pass the incoming signal. Theincoming signal applied by input stage 196 to the ring gate 200 can onlyby passed by the particular tube which is gated open at this particularinstant. As a result, the output of the ring gate 200 takes the form ofthree distinct signals, each of which corresponds to one of the carrierphases which has been transmitted.

At the start of transmission, the correct phase relationship between thetransmitter and the receiver may be provided by establishing a referencephase, such as phase A. To accomplish this, the ring gate circuitry iscaused to run at an incorrect speed until proper phase relationships areestablished. Alternatively, the ring circuitry may be allowed to stopincorrectly, such as by utilizing only two stages until correct phaserelationships are established. If desired, a signal of two alternatingphases can be transmitted to change the ring relation speed or sequenceuntil the zero signal is received on a predetermined circuit. Ingeneral, any of the several expedients listed above may be utilized toestablish proper phase relationships between the transmitter and thereceiver.

It will be apparent to those skilled in the art that many modificationsof the disclosed embodiment of this invention may be made withoutdeparting from the scope thereof which is to be measured by the appendedclaims.

What is claimed is:

1. In a receiver for a single frequency communication wave modulated inkeyed shifts of phase each a proper fraction of a cycle of which thedenominator is a predetermined integer larger than 2,

a receiver for said wave producing voltage peaks corresponding tosimilar peaks present in the wave phase instantly transmitted,

a frequency multiplier generating a wave having voltage peaks coincidentwith voltage peaks of said communication wave in each transmitted phasethereof,

a ring counter circuit connected for stepped operation at the frequencyof said generated wave and having a number of steps to complete a cycleequal to said integer and an output corresponding to each step, and

means selecting and applying to each said output a signal correspondingto each coincidence of wave peaks of said generated wave and saidproduced voltage of the instantly received wave.

2. The method of demodulation of a phase modulated single frequencycommunication wave in which transmitted phases of modulations are each aproper fraction of a cycle, the fraction denominator being an integerlarger than 2, comprising the steps of locally receiving a replica ofsaid wave,

generating therefrom an harmonic wave having voltage peaks coincident intime with voltage peaks of all of said phases when transmitted,

electrically selecting those of said generated peaks which arecoincident with peaks of the instantly received wave, and

indicating in each one of a number of separate outputs equal to saidinteger, the presence of said selected coincident peaks for the durationof said phase of transmission.

3. A receiver for a single frequency communication wave phase modulatedin multiples of one-third cycle to indicate at intervals each of threeinformation indications, comprising receiver means producing a localwave containing in sequence said information indications,

means responsive to said received wave generating an unmodulated signalof three times said frequency and having three groups of voltage peaks,each group being synchronous with peaks of said local wave for apredetermined one of said modulations during the interval received,

three signal switching means each operatively connected for response toconcurrent said voltage peaks of said received wave and the peaks of onesaid group, and

means individual to each said switch means for producing an outputduring the interval of concurrent said peaks thereat, said outputoccurring at each switch means when peaks of the received Wave areconcurrent with peaks of the generated signal group individual thereto.4. In a receiver for a single frequency communication wave modulated inkeyed shifts of phase each a proper fraction of a cycle of which thedenominator is a predetermined integer larger than 2,

a receiver reproducing a voltage signal corresponding to said wave,means generating regular voltage excursions in each cycle of said waveequal in number to said integer arranged adjacently in a sequencecomprising a number of interspersed regular series equal to saidinteger, each series containing excursions corresponding to a series ofexcursions of the received wave for one phase thereof and each seriescorresponding to a different one of said keyed phase shifts,

ring gate means having sequentially conducting stages equal in number tosaid integer, being connected each to respond to concurrence of saidsignal and said generated voltage excursions of one said seriescorresponding to each of the received phases, and to selectively passsaid signal from the stage when said voltage excursions and said voltagesignal are in concurrence,

output means individual to each said stage for passing said signalduring said concurrence, whereby instantly existing conditions of phaseshift are detected and set out in individual outputs respectivelyseparated as to time of occurrence.

5. In a receiver for a constant frequency A.C. voltage wave discretelymodulated in phase shifts each equal to a proper fraction of a cycle ofwhich the denominator is an integer greater than 2, comprising pulsegenerating means excited by said received Wave to generate a compositesequence of pulses comprising a series of pulses at said frequencyconcurrent with corresponding voltages of one said modulated phase ofthe received wave, and an additional like series of pulses, for each ofthe other transmitted phases, the pulses of said composite sequence eachbeing concurrent in time with the corresponding pulse of a transmittedWave of one of said phases,

ring gate coincidence selecting means having a number of conductingstages equal to said integer, being successively actuated one step foreach generated pulse and including a separate output from each stage,

means feeding said pulses of received wave to said ring gate means, and

means coupling pulses of each series when coincident with acorresponding pulse of received wave to a respective said outputaccording to the phase of the wave then being received.

6. A receiver for an information signal transmitted as discrete phasemodulations of a fixed frequency each an exact integral multiple of thereciprocal of an integer greater than 2, comprising receiving meanstuned and energized to produce an alternating current signal of saidfrequency, as modulated,

a local oscillator excited by said signal to oscillate at said frequencytimes said integer each oscillation thereof being in voltage peaksynchronism with only one said phase modulation,

ring gate means having a number of steps in a complete r-ing cycle equalto said integer and an output connection activated individually by eachsaid gate step,

said ring gate means having only a single gate step in conductivecondition at any instant and said conductive step being successivelymoved one step around the ring gate in response to each saidoscillation, and

means applying said signal to each of said steps to provide an output atone said output connection when said oscillation voltage peak of thatstep concurs with a voltage peak of said modulated signal.

7. A receiver for an information signal transmitted as discrete phasemodulations of a fixed frequency each an exact integral multiple of thereciprocal of an integer greater than 2, comprising receiving meanstuned and energized to produce an alternating current signal of saidfrequency, as modulated,

a local oscillator excited by said signal to oscillate at said frequencytimes said integer, each oscillation thereof being in voltage peaksynchronism with the transmitted signal for only one said phase ofmodulation,

ring gate means having a number of steps in a complete ring cycle equalto said integer and an output connection activated individually by eachsaid gate step,

input means connecting said signal to said gate means,

switch means in each said gate step arranged for conduction uponactivation of said step to pass a portion of said signal when said gatestep is conductive.

8. A receiver for a single frequency information signal wherein theinformation is in the form of keyed predetermined alterations of phaseeach an integral multiple of the reciprocal of an integer greater than2, comprising receiving means tuned and energized to produce a receivedwave of said frequency containing said alterations of phase,

a local oscillator excited by the received wave to oscillate at amultiple frequency which is said integer times the frequency of thereceived wave,

ring gate means having gated conducting stages equal in number to saidinteger,

means applying a signal from said oscillator to successively step thering gate one step for each cycle of said multiple frequency,

means applying said received wave to all said stages,

and

output means for each said stage responsive when said stage isconducting to pass a signal whenever the instantaneous phase of saidwave includes a series of voltage peaks with peaks concurrent of saidmultiple frequency for causing conduction in the stage.

9. A receiver for a single frequency information signal wherein theinformation is inthe form of keyed predetermined alterations of phaseeach an integral multiple of the reciprocal of an integer greater than2, comprising receiving means tuned and energized to produce a receivedwave of said frequency containing said alterations of phase,

a local oscillator excited by the received wave to oscillate at amultiple frequency which is said integer times the frequency of thereceived Wave,

ring gate means having output connections equal in number to saidinteger and arranged to pass to each said connection an output spacedapart by said integer times the interval between successive gate inputsignals,

means applying voltage pulses of said oscillator frequency as said inputsignals, thereby to produce a sequence of actuated output conections,

and means applying the received waves to said ring gate for conductionat said conections to register the phase of received wave correspondingto a coin-' cident voltage phase of said multiple frequency at only thatconnection then actuated to pass an output.

10. In a receiver for a single frequency communication signal which isphase shift modulated only in multiples of a phase angle of Where n isan integer greater than 1,

means continuously receiving said signal asphase modulated,

means multiplying the frequency of said signal by a factor of n+1,

ring gate means dividing the multiplied frequency by said factor andselecting which peaks of said multiplied frequency signal correspond involtage to the phase of the instantly received signal, and

means segregating receiver outputs according to said selection ofcorresponding voltage peak phases.

11. In a receiver for a transmitted single frequency communication wavewhich is phase shift modulated only 5 in multiples of a phase angle ofReferences Cited by the Examiner UNITED STATES PATENTS 2,778,933 1/1957Crist 329-5O 2,848,628 8/1958 Altschul 307-885 2,991,354 7/1961 Crafts325-320 3,087,011 4/1963 Boothroyd 178-5.2

30 DAVID G. REDINBAUGH, Primary Examiner.

ALFRED L. BRODY, Examiner.

S. J. GLASSMAN, Assistant Examiner.

1. IN A RECEIVER FOR A SINGLE FREQUENCY COMMUNICATION WAVE MODULATED INKEYED SHIFTS OF PHASE EACH A PROPER FRACTION OF A CYCLE OF WHICH THEDENOMINATOR IS A PREDETERMINED INTEGER THAN 2, A RECEIVER FOR SAID WAVEPRODUCING VOLTAGE PEAKS CORRESPONDING TO SIMILAR PEAKS PRESENT IN THEWAVE PHASE INSTANTLY TRANSMITTED, A FREQUENCY MULTIPLIER GENERATING AWAVE HAVING VOLTAGE PEAKS COINCIDENT WITH VOLTAGE PEAKS OF SAIDCOMMUNICATION WAVE IN EACH TRANSMITTED PHASE THEREOF, A RING COUNTERCIRCUIT CONNECTED FOR STEPPED OPERATION AT THE FREQUENCY OF SAIDGENERATED WAVE AND HAVING A NUMBER OF STEPS TO COMPLETE A CYCLE EQUAL TOSAID INTEGER AND AN OUTPUT CORRESPONDING TO EACH STEP, AND MEANSSELECTING AND APPLYING TO EACH SAID OUTPUT A SIGNAL CORRESPONDING TOEACH COINCIDENCE OF WAVE PEAKS OF SAID GENERATED WAVE AND SAID PRODUCEDVOLTAGE OF THE INSTANTLY RECEIVED WAVE.